Truman succeeded in keeping Stalins hands off of Japan, which if defeated just a month or two later would have been divided into a US controlled, South Japan and a USSR controlled, North Japan, as with Germany until recently and Korea to this very day.
I’ve read that is one of the main reasons we dropped the Fat Man. The message was clear: This was not a “one off” thing.
Yes. And it would be worse than that. The USSR would have controlled a large portion of China, all of Korea as well as much of Japan. Dropping the atom bomb on Japan stopped the USSR in its tracks at the 38th parallel in Korea. They were all set to invade Japan but settled on taking Japanese held territory they already controlled at the time the bomb was dropped. Long ago I worked with an elderly Russian man who lived in China and was taken prisoner by the Japanese. There were lots of Russian enclaves in north China, and they suffered in prison camps. The Russians would have exacted revenge on Japan if they invaded Japan at the end of WWII, far in excess of what could be imagined.